Blood compatibility with polymers

A number of polymer surface parameters, e.g. surface free energy and surface charge, are responsible for blood interaction phenomena. Regarding the correlation of hydrophilidty and thrombocyte adhesion, Ikada et al. determined a maximum of thrombocyte adhesion for a contact angle region between 60 and 80° [95]. Van Wachem et al. showed that the best blood compatibility of polymer blends is achieved for moderate wettability [96]. The influence of polar and dispersive components of the surface tension on blood compatibility was described by Kaelble and Coleman [97,98]. They found that polymers with high dispersive (y ) and low polar components (yP) of surface tension show better blood compatibility than polymers with low dispersive interactions. Furthermore, a nega-... 

X. Wang, N. Yang, Q. Xu, C. Mao, X. Hou, and J. Shen, Preparation of a novel superhydrophobic PMMA surface with nanostructure and its blood compatibility. e-polymers 81,1-8 (2012). 

Hexachlorocyclotriphosphazene (cycHc trimer) is a respiratory irritant. Nausea has also been noted on exposure (10). Intravenous and intraperitoneal toxicity measurements were made on mice. The highest nonlethal dose (LDq) was measured as 20 mg/kg (11). Linear chloropolymer is also beUeved to be toxic (10). Upon organic substitution, the high molecular weight linear polymers have been shown to be inert. Rat implants of eight different polyphosphazene homopolymers indicated low levels of tissue toxicity (12). EZ has been found to be reasonably compatible with blood (13), and has lower hpid absorption than fiuorosihcone. 

Grafting and modification of polymers have been found to have applications in the biomedical field. For example, poly(etherurethane), which has good elastomeric and often mechanical properties and a relatively high compatibility with blood, has been used in the man-... 

Hydrophobic or Hydrophilic Polymers with Excellent Mechanical Properties and Flexibility, Tunable Surface Energy for Cardiovascular Applications. Blood Compatibility ... 

Similarly to the phospholipid polymers, the MPC polymers show excellent biocompatibility and blood compatibility [43—48]. These properties are based on the bioinert character of the MPC polymers, i.e., inhibition of specific interaction with biomolecules [49, 50]. Recently, the MPC polymers have been applied to various medical and pharmaceutical applications [44-47, 51-55]. The crosslinked MPC polymers provide good hydrogels and they have been used in the manufacture of soft contact lenses. We have applied the MPC polymer hydrogel as a cell-encapsulation matrix due to its excellent cytocompatibility. At the same time, to prepare a spontaneously forming reversible hydrogel, we focused on the reversible covalent bonding formed between phenylboronic acid and polyol in an aqueous system. 

Ikada and coworkers also studied the blood compatibility and protein denaturation properties of heparin covalently and ionically bound onto polymer surfaces [513], Both types of bound heparin gave deactivation of the coagulation process. Clotting deactivation was attributed to a heparin/ antithrombin III complex by covalently bound heparin which gave adsorbed protein denaturation and platelet deformation as compared with lack of these features with ionically bound heparin. 

Problems of desorption and loss of activity encountered with natural heparin have led numerous workers to explore synthetic heparin-like polymers or heparinoids, as reviewed by Gebelein and Murphy [475, 514, 515]. The blood compatibility of 5% blended polyelectrolyte/polyfvinly alcohol) membranes was studied by Aleyamma and Sharma [516,517]. The membranes were modified with synthetic heparinoid polyelectrolytes, and surface properties (platelet adhesion, water contact angle, protein adsorption) and bulk properties such as permeability and mechanical characteristics were evaluated. The blended membrane had a lower tendency to adhere platelets than standard cellulose membranes and were useful as dialysis grade materials. 

Studies to elucidate the correlation between the structure of the polymer gels and their blood compatibility were carried out by means of 13C-NMR (for mobility of the PEG chains) and H-NMR and DSC (for the effect of water on their properties). Results are shown in Table 7. By comparing these results with one another, Tanzawa et al. concluded that material surfaces with the highest fraction of water molecules of intermediate mobility exhibit the best blood compatibility. This was supposed to come from a similar mobility of the intermediate water compared to that of oligosaccharides on the outermost surface of the cell... 

The long quest for blood-compatible materials to some extent overshadows the vast number of other applications of polymers in medicine. Development and testing of biocompatible materials have in fact been pursued by a significant number of chemical engineers in collaboration with physicians, with incremental but no revolutionary results to date. Progress is certainly evident, however the Jarvik-7 artificial heart is largely built from polymers [34]. Much attention has been focused on new classes of materials, such... 

Attempts to develop new base polymers which are more compatible with blood. 

Applications to polymer chemistry have also been proposed. Interestingly. the adhesion toward itself. Al or stainless steel, of polythene or TeHon with epoxyresins adhesives is considerably improved by a glow discharge polymerization of methane (or etheiie. ethyne) on the polymer surface, CH4 giving the best results (33). Such a modification of polymer surfaces has also received attention within the scope of modifying poly mer membrane compatibility with blood for medical applications. Various o nic compounds (even CH4 > have been studied in this context, where an ultrathin layer (< 1000 is sufficient to alter blood compatibility 134). 

In addition to microelectronic and optical applications, polymers deposited using thermal and plasma assisted CVD are increasingly being used in several biomedical applications as well. For instance, drug particles microencapsulated with parylenes provide effective control release activity. Plasma polymerized tetrafiuoroethylene, parylenes and ethylene/nitrogen mixtures can be used as blood compatible materials. An excellent review of plasma polymers used in biomedical applications can be found in reference 131. 

Wilson, at Bishop College, and Eberhart and Elkowitz at University of Texas (27) have irradiated a silicone substrate in the presence of chloromethylstyrene monomer to produce a reactive graft polymer that can be quarternized with pyridine and reacted with sodium heparin to produce a thromboresistant heparinized product that has a higher blood compatibility than the untreated silicone. The same group has used essentially the same methods to create a heparin grafted polyethylene surface. 

Implanted polymeric materials can also adsorb and absorb from the body various chemicals that could also effect the properties of the polymer. Lipids (triglycerides, fatty acids, cholesterol, etc.) could act as plasticizers for some polymers and change their physical properties. Lipid absorption has been suggested to increase the degradation of silicone rubbers in heart valves (13). but this does not appear to be a factor in nonvascular Implants. Poly(dimethylsiloxane) shows very little tensile strength loss after 17 months of implantation (16). Adsorbed proteins, or other materials, can modify the interactions of the body with the polymer this effect has been observed with various plasma proteins and with heparin in connection with blood compatibility. 

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